LATTICE THEORY OF POLYMER-SOLUTIONS WITH ENDGROUP EFFECTS

We present a unified lattice theory for a binary solution where endgro ups are treated differently from middle groups. This is a simple examp le of a triblock and the present study provides a starting point for s tudying a general triblock system. We replace the original homogeneous lattice by a Bethe lattice of the same coordination number as the ori ginal lattice. The model is solved exactly on the Bethe lattice. The r esulting solution goes beyond the random mixing approximation and prov ides us with an approximate theory of the model on the regular lattice . The contributions of endgroups on various thermodynamic properties o f a binary solution are investigated in a quantitative way using the t heory. In particular, our theory predicts that contributions to the en ergy are more important than to the entropy. (C) 1997 American Institu te of Physics.